With the bodybuilders you can make the arguement that they are actually underweight and skirting being unhealthy because of the harsh dieting they do in the lead-up to a show/competition/photoshoot to get their skin to go tight to show off their guns better.

But in terms of an illustrative effect in a render you would lean towards that "Show Build" rather than that of your average regular gym visitor to underline the theme/idea of ultra-fittness/athleticism.

Cheers